DC-to-AC power converters are known by the one skilled in the art and are typically used in the telecommunication industry. For historical reasons, the loads in this industry indeed typically need an AC input voltage whereas the energy is often delivered by a battery that provides a DC voltage, while a battery as energy supplier is often chosen in low power applications.
FIG. 1 shows an example of a DC-to-AC power converter 1 known by the one skilled in the art. Such a converter is able to convert a DC voltage at its main input 10 into an AC voltage at his main AC output 20. As illustrated in FIG. 1, DC-to-AC power converters known by the one skilled in the art typically comprise a first DC-to-DC converter 30 that generally has two functions: firstly, adapting (e.g. increasing) a DC voltage provided by a battery connected at the main DC input 10; and secondly, galvanically isolating this low voltage battery, and so protecting it, from disturbances or faults coming from the main AC output 20. In order to achieve this second function, the first DC-to-DC converter 30 has to be isolated (see double strike). A tank capacitor 40 is typically connected in between the first DC-to-DC converter 30 and a DC-to-AC converter 50. This second converter 50 provides at the main AC output 20 the required sinusoidal AC voltage.
DC-to-AC power converters such as the one shown in FIG. 1 present different losses. As a consequence, the efficiency of such converters is not optimal.
Document JP 11 206133 A discloses a AC-to-AC power converter equipped with a current-type power converter and a voltage-type power converter. In the current-type power converter, a DC current outputted from a rectifier, converting an AC output to a DC current, is smoothed by a reactor and supplied to an inverter. The DC current is converted by the inverter to a 120° current flow square wave-type AC current by on-off control of a switching element of the inverter constituted of semiconductor elements. Thus the inverter circuit supplies a main current to a load, such as a 3-phase AC current to an induction motor. The voltage-type power converter is connected with the AC output terminal of the current-type power converter via a reactor, converts a DC voltage obtained from an input side capacitor to an AC voltage by on-off control of a switching element of an inverter constituted of semiconductor elements, and controls the current to be supplied to the load from the current-type power converter so as to obtain a sine wave. The output current phase of the current-type power converter is switched by the interphase voltage of the voltage-type power converter. The problem solved is to reduce power loss in semiconductor elements constituting an inverter circuit and current increase at the time of rapid change of a load.
Document EP 2 770 624 A1 discloses a method and an apparatus for producing a three-phase current to a three-phase output from a DC voltage input. The method comprises producing a positive current, a negative current, and an intermediate current by using switching converters. The produced positive current follows a path of a highest phase of a sinusoidal three-phase signal at a given time, the produced negative current follows a path of a lowest phase of the three-phase signal at the given time, and the produced intermediate current follows a path of a phase of the three-phase signal between the highest and the lowest phase at the given time. The produced currents are switched to each phase conductor of the three-phase output in sequence so that phase currents of the three-phase current are formed in the output conductors.